list 创建一个 data.frame，其中一列是一个列表
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Create a data.frame where a column is a list
提问by flodel
I know how to add a list column:
我知道如何添加列表列：
> df <- data.frame(a=1:3)
> df$b <- list(1:1, 1:2, 1:3)
> df
a b
1 1 1
2 2 1, 2
3 3 1, 2, 3
This works, but not:
这有效，但无效：
> df <- data.frame(a=1:3, b=list(1:1, 1:2, 1:3))
Error in data.frame(1L, 1:2, 1:3, check.names = FALSE, stringsAsFactors = TRUE) :
arguments imply differing number of rows: 1, 2, 3
Why?
为什么？
Also, is there a way to create df(above) in a single call to data.frame?
另外，有没有办法df在一次调用中创建（上面）data.frame？
回答by Ben Bolker
Slightly obscurely, from ?data.frame:
有点晦涩，来自?data.frame：
If a list or data frame or matrix is passed to ‘data.frame' it is as if each component or column had been passed as a separate argument (except for matrices of class ‘"model.matrix"' and those protected by ‘I').
如果将列表或数据框或矩阵传递给 'data.frame'，就好像每个组件或列都作为单独的参数传递（除了类 '"model.matrix"' 的矩阵和受 'I '）。
So
所以
data.frame(a=1:3,b=I(list(1,1:2,1:3)))
seems to work.
似乎工作。
回答by mnel
If you are working with data.tables, then you can avoid the call to I()
如果您正在使用data.tables，那么您可以避免调用I()
library(data.table)
# the following works as intended
data.table(a=1:3,b=list(1,1:2,1:3))
a b
1: 1 1
2: 2 1,2
3: 3 1,2,3
回答by Deleet
data_frames (variously called tibbles, tbl_df, tbl) natively support the creation of list columns using the data_frameconstructor. To use them, load one of the many libraries with them such as tibble, dplyror tidyverse.
data_frames（也称为tibbles, tbl_df, tbl）本机支持使用data_frame构造函数创建列表列。要使用它们，请使用它们加载众多库之一，例如tibble,dplyr或tidyverse。
> data_frame(abc = letters[1:3], lst = list(1:3, 1:3, 1:3))
# A tibble: 3 × 2
abc lst
<chr> <list>
1 a <int [3]>
2 b <int [3]>
3 c <int [3]>
They are actually data.framesunder the hood, but somewhat modified. They can almost always be used as normal data.frames. The only exception I've found is that when people do inappropriate class checks, they cause problems:
它们实际上是data.frames在引擎盖下，但有些修改。它们几乎总是可以正常使用data.frames。我发现的唯一例外是，当人们进行不适当的类检查时，会导致问题：
> #no problem
> data.frame(x = 1:3, y = 1:3) %>% class
[1] "data.frame"
> data.frame(x = 1:3, y = 1:3) %>% class == "data.frame"
[1] TRUE
> #uh oh
> data_frame(x = 1:3, y = 1:3) %>% class
[1] "tbl_df" "tbl" "data.frame"
> data_frame(x = 1:3, y = 1:3) %>% class == "data.frame"
[1] FALSE FALSE TRUE
> #dont use if with improper testing!
> if(data_frame(x = 1:3, y = 1:3) %>% class == "data.frame") "something"
Warning message:
In if (data_frame(x = 1:3, y = 1:3) %>% class == "data.frame") "something" :
the condition has length > 1 and only the first element will be used
> #proper
> data_frame(x = 1:3, y = 1:3) %>% inherits("data.frame")
[1] TRUE
I recommending reading about them in R 4 Data Science(free).
我建议在R 4 Data Science（免费）中阅读它们。
